The American Journal of Tropical Medicine and Hygiene -
Volume 48,
Issue 2,
February 1993

Volume 48,
Issue 2,
February 1993

During this time of war and famine in Somalia, disease threats are encyclopedic both for Somalis and visitors. Malnutrition will amplify the magnitude and severity of endemic tropical infectious diseases. Necessary crowding around lifesaving food distribution centers could turn focal infectious disease outbreaks into large epidemics.

The assignment of significant numbers of members of the U.S. Armed Forces to Somalia in Operation Rescue Hope will bring Americans into contact with a remarkable variety of infectious diseases and other potential health threats. This issue opens with a brief but very informative survey of the more prominent of these issues that must be faced by preventive medicine detachments involved in the effort. The readers of the Journal owe a debt of gratitude to Drs. Larry Laughlin and Llewellyn Legters and their colleagues at the Uniformed Services University of the Health Sciences and the Naval Medical Research Institute for rapidly developing this important review. The variety of potential medical problems in this unfortunate country is large and frightening, and it is important that our readers be informed concerning this important issue.

The mechanisms by which the hemoglobin genotype AS protect against severe malaria are not fully understood. We have investigated the possibility that protection might be achieved through an inability of red blood cells (RBC) with the AS genotype to form rosettes with RBC infected by Plasmodium falciparum. No evidence was obtained to support this hypothesis because RBC with the AS genotype formed rosettes with wild isolates of P. falciparum as readily as RBC with the AA genotype. However, the previous finding that parasitized RBC form rosettes more readily with RBC belonging to group A or B than with RBC belonging to group O was confirmed even in fresh clinical isolates.

An understanding of processes that predispose pregnant women, and in particular primigravidae, to malaria infection is essential to improve malaria management in pregnancy. Lymphoproliferative responses to malaria-specific (F32, 190L, and 190N) as well as other antigens (Candida and purified protein derivative [PPD]) were examined in the peripheral and placental blood of 102 Gambian women at the time of delivery. The lymphoproliferative responses of placental cells were poor to all antigens compared with those of peripheral blood (Candida P < 0.001, PPD P < 0.001, F32 P = 0.008, 190L P = 0.003, and 190N P = 0.10). Reduced proliferative capacity of placental mononuclear cells may contribute to heavy parasite colonization of this organ. Proliferation to malarial and PPD but not Candida antigens was selectively suppressed in peripheral and placental blood of primiparae relative to multiparae (F32 P = 0.07, 190L P = 0.09, 190N P = 0.007, PPD P = 0.09). Autologous plasma contained factors that suppressed lymphoproliferative responses to the same series of antigens to which the primiparae responded poorly (F32 P < 0.001, 190L P < 0.001, 190N P < 0.001, PPD P = 0.03). Malarial antibody levels were comparable among women of different parities and between peripheral and placental blood. Primigravidae may be more susceptible to malaria because of unique physiologic factors, such as higher levels of circulating immunosuppressive corticosteroids (P < 0.001), rather than differences in levels of acquired immunity.

Using glycol methacrylate in conjunction with avidin-biotin-peroxidase complex techniques, we studied the contribution of T cell subsets to tissue inflammation during acute Trypanosoma cruzi infection. Two mouse/parasite model systems whose parasitology and pathology behaved differently were used. In C57Bl/6J mice infected with the T. cruzi Brazil strain, the levels of parasitism in blood and tissue (myocardial and skeletal muscle) reached a maximum at week 6 and decreased rapidly thereafter. Inflammatory responses in tissue corresponded with the parasitism, but decreased in intensity more gradually than that of parasitism. The T lymphocytes (Thy 1.2+) were found to be the major lymphocyte population in inflammatory cardiac and skeletal muscles (64.6–81.2%) at both three and six weeks postinfection. Among T cells, CD8+ cells (47.0–58.9%) significantly outnumbered CD4+ cells (9.3–18.6%). The number of B cells (0–1.0%) and macrophages was low. Experiments using C3H/HeSnJ mice infected with the Sylvio X10/4 clone of T. cruzi at 30 days postinfection resulted in similar findings except for a higher CD8+:CD4+ ratio. The primary finding of this study is that Thy 1.2+CD8+CD4- T lymphocytes are the major cell population in both heart and skeletal muscle in acute murine T. cruzi infection. The predominance of CD8+ T cells coincident with the decrease in the tissue parasite burden suggests a role for CD8+ T cells in the control of T. cruzi at the level of the infected cell.

Human T lymphotropic virus type-1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is endemic in tropical areas and in southwestern Japan, and has now been identified among risk groups in the United States and some European countries. Patients with HAM/TSP may also have T lymphocyte alveolitis related to the HTLV-1 infection. To quantify proportions of HTLV-1-infected cells, a fragment of HTLV-1 proviral DNA was amplified from peripheral blood mononuclear cells (PBMC) and bronchoalveolar lavage (BAL) cells obtained from patients with HAM/TSP, non-HAM/TSP HTLV-1 carriers with chronic pulmonary inflammation, and asymptomatic HTLV-1 carriers. The proportion of HTLV-1-infected cells in PBMC from patients with HAM/TSP was much higher (3–30%) than that from asymptomatic HTLV-1 carriers (mostly < 1%), based on findings with the quantitative polymerase chain reaction. In non-HAM/TSP carriers with chronic pulmonary inflammation, HTLV-1-infected cells in PBMC were also increased, but not as markedly as that seen in patients with HAM/TSP. Integration of HTLV-1 was also noted in BAL cells from patients with HAM/TSP or non-HAM/TSP carriers with chronic pulmonary inflammation. However, in patients with HAM/TSP, there was a marked increase in HTLV-1-infected cells in the lung (7.5–30% of BAL cells), as compared with findings in non-HAM/TSP carriers (< 5%). These results suggest that increased HTLV-1 proviral DNA loading may play an important role in the development of T lymphocyte alveolitis and myelopathy in patients with HAM/TSP.

To compare the efficacy and tolerability of various combinations of low- and high-dose ivermectin and diethylcarbamazine (DEC), 59 persons with Wuchereria bancrofti microfilaremia were enrolled in a double-blinded six-arm clinical trial in Leogane, Haiti. On day 1, study participants were treated with low clearing doses of ivermectin, DEC, or placebo; on day 5 they received 200–400 µg/kg of ivermectin or 6 mg/kg of DEC. Adverse reactions, which were generally mild, occurred more frequently with ivermectin than with DEC. One year after treatment, the geometric mean microfilarial density returned to 0.9% of pretreatment levels for persons who received a total of 420 µg/kg of ivermectin. This rate was significantly lower than 5.6% for persons who were treated with 220 µg/kg of ivermectin (P = 0.02) and 9.3% for those receiving 6 or 7 mg/kg of DEC (P = 0.006). Persons treated with a clearing dose of ivermectin followed by 6 mg/kg of DEC also had low microfilarial densities (1.7% of pretreatment levels), suggesting an additive or synergistic effect of the two drugs. The addition of a clearing dose neither reduced the severity of adverse reactions nor improved the efficacy of high-dose ivermectin. Community-based intervention trials are now warranted to determine the feasibility and effectiveness of mass chemotherapy with single high-dose ivermectin for the prevention and control of lymphatic filariasis.

A study was carried out in southeastern Gabon to evaluate the tolerance and efficacy of single high doses of ivermectin in 31 Loa loa-infected subjects with low-to-moderate parasitemia (7–7,700 microfilaria/ml). The first group of 16 subjects received 300 µg/kg of ivermectin and, seven days later, a second group of 15 received 400 µg/kg. Complete clinical and biological monitoring was carried out during the first 10 days post-treatment and again after one and three months. All subjects continued with their usual activities during the study. The clinical tolerance of treatment was very good, and except in one case, only mild adverse reactions were observed, with pruritus being the most common symptom. There were no significant changes in blood or urine function test results or in hematologic results, except for a pronounced eosinophil reaction. The 400 µg/kg dose of ivermectin equaled or surpassed in tolerance that of 300 µg/kg dose. After treatment, L. loa microfilaremia decreased rapidly to less than 9% of the pretreatment value by day 10. This decrease was enhanced with the 400 µg/kg dose, although differences between the two groups diminished slightly with time. At 100 days post-treatment, the microfilaremia was still at less than 10% of the initial values in the two groups, which may indicate an effect of ivermectin on the adult worms.

To examine the effect of iron chelation against human malaria, 37 Zambians with asymptomatic Plasmodium falciparum infections were randomly assigned to 72-hr infusions of desferrioxamine B or placebo. Mean concentrations of ring forms decreased significantly with desferoxamine B (P < 0.001) but not with a placebo. Over seven days of observation, mean parasite concentrations remained at the initial levels in six individuals originally given placebo, but decreased promptly with administration of desferrioxamine B (P = 0.001). Mean parasitemia was significantly lower for up to four weeks in 16 subjects treated with desferrioxamine B when compared with the eight who had received placebo only (P = 0.027). We conclude that iron chelation has antiplasmodial activity and may offer a new therapeutic strategy for falciparum malaria.

A specific serodiagnostic test for onchocerciasis has been a priority objective of the World Health Organization. Fragments of cDNA encoding Onchocerca volvulus antigens selected on the basis of their specificity for this parasite were subcloned into a protein purification and expression system. No individual recombinant antigen showed a high sensitivity in an enzyme-linked immunosorbent assay because of heterogeneity in the response of O. volvulus-infected individuals. However, a cocktail of three recombinant proteins showed 96% sensitivity with 100% specificity, compared with 99% sensitivity and only 59% specificity against a crude O. volvulus extract. The sensitivity of detection of individual antigens varied between sera taken from individuals from different geographic areas infected with O. volvulus, but when used as a cocktail, all but one of the microfilariapositive individuals from all the geographic areas studied were detected. Recombinant probes provide a practical basis for specific diagnostic tests for helminth infections.

This report describes an enzyme assay for the detection of Plasmodium falciparum. The assay is based on the observation that the lactate dehydrogenase (LDH) enzyme of P. falciparum has the ability to rapidly use 3-acetyl pyridine NAD (APAD) as a coenzyme in the reaction leading to the formation of pyruvate from lactate. Human red blood cell LDH carries out this reaction at a very slow rate in the presence of APAD. We measured the development of APADH and found that the formation of this product could establish the basis of an assay that detected the presence of P. falciparum from in vitro cultures at parasitemia levels of 0.02%. We also had occasion to use this assay with clinical samples. We found a correlation between levels of parasitemia and the activity of parasite LDH. Parasite LDH (pLDH) activity could be measured in blood hemolysates and in plasma and serum from patients with malaria. We used the serum assay for pLDH and followed the level of pLDH in a patient with cerebral malaria prior to antimalarial treatment and during the recovery period. From these initial studies, it is evident that the measurement of pLDH has a correlation with parasitemia and may offer a method that can be developed into a simple test for the detection of Plasmodium parasitemia.

This study evaluated a nonisotopic DNA assay kit for diagnosing Plasmodium falciparum malaria in an area of Madagascar where all Plasmodium species of human malaria are present and where malaria is endemic. Blood samples from 440 healthy children and 20 healthy adults were processed and assayed in a single day in a blind protocol. The parasitemia levels of the four Plasmodium species were determined by microscopic examinations and by counts of numbers of malaria parasites per 1,000 white blood cells. Relative to P. falciparum infections, the DNA assay results agreed with those of microscopy for 207 positive and 239 negative samples; two samples were scored as positive by the DNA probe that were not detected by microscopy, and 12 samples were scored as positive by microscopy but were not detected by the assay. Relative to microscopy, the sensitivity of the assay was 95%, the specificity was 99%, and the effective sensitivity threshold of the DNA probe assay was approximately 30 parasites/mm3 of blood. The assay did not detect infections with either P. vivax, P. malariae, or P. ovale alone, but detected mixed infections of P. falciparum with either P. vivax or P. ovale. With this nonisotopic DNA probe assay, we were able to process large numbers of samples efficiently and to detect P. falciparum malaria infections with high sensitivity and specificity in a population that did not display overt disease symptoms.

This study was carried out on 170 children admitted to the University Hospital of Brazzaville (Congo) for cerebral malaria between January 1, 1988 and June 30, 1989. The selection criteria were 1) unarousable coma, cerebrospinal fluid without microorganisms or a marked cellular reaction, and the absence of other causes, and 2) that the children lived in Brazzaville. The case fatality rate was 15%. In 75% of the cases, death occurred within the first 48 hr. The prognosis worsened with the stage of the coma and a younger age. At discharge from the hospital, 9% of the cases presented with sequelae. The postcerebral malaria mortality was high; indeed, death occurred in six (7%) of 90 children discharged from the hospital whose parents were contacted between nine and 27 months later. Two deaths were directly related to neurologic sequelae. Among the 58 children examined under satisfactory conditions between nine and 27 months (mean 16.9 months) after discharge, 50% (3 of 6) still presented with attenuated forms of the sequelae observed immediately after the episode of cerebral malaria (cortical blindness had regressed completely, unlike ataxia and loss of balance). Disorders that may have been related to the episode of cerebral malaria were observed in 31% of these 58 cases.

We measured the levels of interferon alpha (IFNα) in the sera of Thai children hospitalized with dengue hemorrhagic fever (DHF) or dengue fever (DF) to examine the role of IFNα in dengue virus infections of humans. The percentage of patients who had detectable levels of IFNα (≥ 3 U/ml) was higher in patients with DHF (80%, P < 0.001) and in patients with DF (60%, P < 0.001) than in healthy Thai children (7%). The levels of IFNα were higher in patients with DHF and in patients with DF on the first few days after the onset of fever than in healthy Thai children. The average levels of IFNα in patients with DHF were high two days before defervescence, decreasing gradually until the day of defervescence. There was a subset of patients with DHF who had increasing levels of IFNα after defervescence. However, the levels of IFNα in patients with DF were not high after fever subsided. The levels of IFNα were not different among children with DHF grades 1, 2 and 3. Among patients with DHF, T lymphocytes were activated to a higher degree in high IFNα producers than in low IFNα producers. These results indicate that similarly high levels of IFNα are produced in vivo during the acute stages of DHF and DF, and that high levels of IFNα remain after fever subsides in some patients with DHF, but not in patients with DF.

There have been several recent reports on the high prevalence of serum antibodies to human T lymphotropic virus-1 (HTLV-1) in isolated populations residing in the coastal areas and highlands of Papua New Guinea. In the absence of significant cases of clinical disease, it has been surmised that this reactivity might be the consequence of serologic recognition of yet undefined human retroviruses or parasite antigens. These observations prompted an investigation of the prevalence of anti-HTLV-1 antibodies among members of the Ngalum tribe that dwells in a secluded highland valley in the eastern Jayawijaya Mountains of Irian Jaya, Indonesian New Guinea. Of 165 tribespeople, 85 (52%) were positive for IgG antibodies to HTLV-1 in an indirect enzyme-linked immunosorbent assay. Eighty-two were more than 10 years of age. On the Western blot, all positive sera reacted strongly with the p19 core antigen, but recognition of the envelope antigens, gp46 and gp21, was conspicuously absent. Thirty-four of the 85 villagers with these indeterminant blots had active Plasmodium falciparum infections, but antibody absorption studies with HTLV-1 and P. falciparum erythrocytic stage antigens failed to confirm suspected serologic cross-reactivities. Thirty-three others had acute malaria and/or high titers of anti-malaria antibodies but were seronegative for HTLV-1. We suspect that indeterminant Western blots for HTLV-1 reflect antibody responses to related latent retroviruses that are activated as a consequence of immunosuppression following malaria infection and chloroquine therapy.

To study the relationship between hepatocellular carcinoma (HCC) and hepatitis C virus (HCV), sera from 178 patients with HCC and 194 blood donors from Maputo, Mozambique were tested for antibodies to HCV (anti-HCV) using a second generation enzyme-linked immunosorbent assay and a confirmatory test with six synthetic peptides as reagents. The presence of hepatitis B surface antigen (HBsAg) was tested using an enzyme immunoassay. The prevalence of anti-HCV was higher in patients with HCC than in controls, but the difference was not significant after adjustment for age. Therefore, this difference reflected a difference in the age structure between the two groups. The prevalence of HBsAg was higher in patients with HCC than in controls. There was a negative association between anti-HCV and HBsAg in patients with HCC that was not significant after adjustment for age. These serologic results, which contrast with previous reports, show the need for further studies on the relationship between HCC and HCV using second generation serologic tests and molecular biology techniques.

A study of acute diarrhea was conducted from 1985 to 1987 among U.S. military personnel participating in routine shipboard exercises in South America and West Africa and ground troops deployed to coastal Ecuador. An enteropathogen was identified in 146 (51%) of 289 acute cases of diarrhea. Enterotoxigenic Escherichia coli, found in 50 (17%) patients with diarrhea, was the most commonly identified enteropathogen. Viral enteropathogens were also found in a high percentage of acute cases of diarrhea: rotavirus was detected in 11% of the patients and Norwalk virus infection in 10%. Most enteric pathogens were acquired in equal frequencies in South America and West Africa, except for rotavirus infection which was identified more often in West Africa and enteroaggregative E. coli infection which was identified more often in South America. Bacterial enteropathogens were frequently resistant to trimethoprim/sulfamethoxazole, but no resistance to quinolone drugs was observed, indicating that quinolone drugs have become important agents for the treatment of diarrhea in South America and West Africa.

We report the results of a comparison of several epidemiologic and ecologic parameters affecting the incidence and seroprevalence of Mediterranean spotted fever (MSF) in northern, central, and southeastern Marseille, an area endemic for this disease. In northern Marseille, the incidence of hospitalized patients with MSF was 24.2/100,000 persons compared with 9.8/100,000 and 8.8/100,000 for the central and southeastern regions, respectively. The seroprevalence in sera from blood donors, determined by microimmunofluorescence and confirmed by Western blot assays, was higher in the northern region than in the other two areas (6.7% versus 3.6% and 2.4%, respectively). This higher prevalence of MSF in the northern part of the city may be related to a greater tick exposure due to a higher number of dogs (32.6/100 inhabitants versus 28.4/100 and 27.2/100 in the central and southeastern regions, respectively) and a higher rate of infection of dogs in the northern region (51.4% versus 43.5% and 39.9%, respectively). The ratio of spotted fever group rickettsia-infected ticks was similar in both the northern and southeastern areas (14.8% and 13.4% respectively), but lower in the central area of the city (8.9%), leading to a higher risk of having MSF after a tick bite in the northern and southeastern parts of Marseille.

Three rickettsial strains isolated from Dermacentor marginatus ticks in southern France in 1991 were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting with polyclonal mouse antisera, microimmunofluorescence serologic typing, and the polymerase chain reaction followed by analysis of restriction fragment length polymorphisms. By these methods, the isolates appear to be identical to the spotted fever group rickettsia, Rickettsia slovaca, which has so far been found only in Czechoslovakia. The fact that this rickettsial strain of unknown pathogenicity may occur in the same regions where R. conorii is endemic is of particular epidemiologic importance.

Thirty-three cases of locally acquired murine typhus were reported in Los Angeles County residents from May 1984 through February 1988. Only eight cases were reported over the previous 20-year period. Thirty (91%) cases resided within a suburban area encompassing approximately 50 km2 in northcentral Los Angeles or had contact with an animal from this area. Serologic testing (complement fixation and indirect fluorescent antibody) of selected animals in close association with human cases revealed a high prevalence of seropositivity among domestic cats and opossums. Nine (90%) of 10 resident cats tested had demonstrable antibody titers compared with none (0%) of 20 cats from a control area (P < 0.001). Suburban typhus cases were more likely than neighborhood controls to own a cat or dog (odds ratio = 6.9, 95% confidence interval = 1.8, 25.9, P = 0.002). Sixteen (42%) of 38 opossums trapped in close proximity to the residences of cases were seropositive versus none (0%) of 36 opossums from control areas (P < 0.001). A low frequency (2.8%) of seropositivity was found in commensal rodents, and the classic vector of murine typhus, Xenopsylla cheopis, was not found. Ectoparasite indices from seropositive opossums revealed heavy infestations with the cat flea, Ctenocephalides felis (mean flea count = 104.7), a species that readily bites humans. These data provide evidence that a suburban focus of murine typhus exists in Los Angeles that differs substantially from the classic transmission cycle, and that cats, opossums and C. felis may play an important role in the occurrence of human cases.